Generally speaking the physical size of objects (i.e., an object's dimensions) may be measured automatically and without contact with a dimensioning system. These dimensioning systems typically rely on a range sensor to determine the range of points on an item. The item's size may then be computed by comparing the range of the individual points on the item. The range sensor may use ultrasonic, radio-frequency (RF), or optical signals to detect range. One such optical range sensor employs time-of-flight (TOF) measurements to measure range.
The time-of-flight (TOF) sensors offer advantages over other optical range sensors (e.g., structured light or stereo vision). One advantage of the TOF sensor is its simplicity. There are no moving parts, and the entire system may be made compact, as there are no special geometries required for sensing range. Also, the sensing and calculation of the range is relatively straight forward and requires small amount of processing power compared to other sensors. This implies a reduced power requirement and could lead to a faster dimensioning result. These advantages make TOF dimensioning systems better suited for non-fixed (i.e., mobile or handheld) dimensioning applications.
The TOF dimensioning system is not without its limitations, however. For example, a TOF sensor senses the range of an item of interest by first illuminating a scene (i.e., field of view) with a beam of light. If the field of view is large compared to the item of interest, then the light beam may reach the item of interest along several different paths. Some paths, for example, may be experience one or more reflections prior to reaching the item of interest. This is known as multipath and leads to a distorting in the range measurement, which in turn leads to dimensioning errors. Light from a reflected path may suggest that the distance to the item of interest (i.e., range) is greater than the actual physical distance. Some means of controlling the multipath distortion is necessary.
Controlling the environment that an item of interest is measured in is one approach. Here, reflections from the background may be minimized and the placement of items may be carefully controlled. In addition, the size and shape of items may be constrained. While these measures might work for a fixed installation, it would not be practical for most mobile dimensioning applications (e.g., package delivery and pickup). In these applications, neither the environment (e.g., warehouse) nor the item of interest (e.g., the package) may be controlled.
A general need exists for a dimensioning system suitable for mobile environments. A time-of-flight (TOF) dimensioning system is suitable but may suffer from multipath distortion. A specific need, therefore, exists for a TOF dimensioning system with adaptable multipath interference suppression to facilitate the accurate dimensioning of a variety of items in a variety of environments.